1. Technical Field of the Invention
The invention relates to a sensor for continuously releasing a liquid, especially a lubricant, over an adjustable period of time. The liquid is ejected from a reservoir by a moveable working plunger. The working plunger is moved with the driving force transmitted from a power transmitter, said power transmitter being mechanically connected to a brake plunger which counteracts the driving force with a brake force by reducing the volume of a chamber filled with a paste-like liquid and ejecting the liquid.
2. Description of the Prior Art
Such sensors are known, for example, from Federal Republic of Germany Patent Application No. 195 09 247. They are used for the continuous and measured release of liquids over a long period of time which is adjustable and, as a rule, ranges over several months. Their most important area of application is the release of substances for permanent lubrication of bearings. The released liquid""s viscosity can be comparatively greatxe2x80x94as, for example, in the case of lubricant greasesxe2x80x94and extend to the viscosity of plastic mass. A force generated by a spring presses the liquid, especially the lubricant, from a reservoir. To achieve a continuous, nearly uniform release, the spring force is compensated by a counter-force which is generated to press a paste-like liquidxe2x80x94especially a silicone mixturexe2x80x94from a chamber. Upon increasing the spring""s relief rate, the counter-force increases so that, upon a specific relief rate, a balance of forces is established on the spring. Thus, a specified period of discharge results, the adjustment of which presently entails considerable expenditure. There are various possibilities for this, such as replacing the spring, replacing the chamber causing the counter-force, or the paste-like liquid. All these methods have in common that they are rather time-consuming and cannot be performed without the corresponding replacement elements on location at the customer""s place of business.
The invention is thus based on the task of providing a sensor whose discharge period is swiftly adjustable by auxiliary means which are easy to carry along.
This task is solved according to the invention such that the paste-like liquid is pressed through a tube that can be cut through.
According to the proposal, the flow resistance is formed by a tube which can be shortened to adjust the discharge period. The mode of action is as follows: the shorter the tube, the smaller the counter-force acting against the driving forcexe2x80x94at a given driving speed, i.e. at a given rate of flow through the tube. Since the counterforce increases due to the flow resistance at an increasing drive speed, a balance of forces is achieved at a higher speed. Then, the discharge process runs faster. By cutting through the tube, thus accordingly shortening the tube, the discharge period is continuously adjustable by simple means and with little time required. Here, the brake plunger can be connected directly or indirectly with the power transmitter, for example, via the working plunger. xe2x80x9cTubexe2x80x9dxe2x80x94within the meaning of the inventionxe2x80x94is understood to mean an oblong body in whose longitudinal direction the liquid is moving. Its cross-section may be random, for example in the form of a circle or a polygon. On the inside, the tube may be additionally provided with resistance bodies. It is also possible to attach several tubes on the chamber which can all be shortened, if necessary, for adjusting the discharge period. Conceivable are rigid or flexible tubes, the last mentioned having the advantage that they can be bent or even rolled up. Thus, upon shortening over a greater length, the downstream front end of the tube can be positioned precisely to enable a defined collection of the discharging paste-like liquid. The great length here enables great adjustment precision and a wide adjustment interval.
In one embodiment of the invention, the tube has a constant cross-section over its total length. In this case, the resulting counter-force is nearly proportional to the length of the tube and, in a laminar flow, it is also approximately proportional to the flow-through speed. From this results an approximate proportionality between discharge period and tube length which considerably simplifies the adjustment.
However, the tube diameter may also change; it may especially decrease in the paste-like liquid""s direction of flow. The shorter the tube, the smaller the minimum flow-through cross-section. Upon shortening the tube, the discharge period thus decreases disproportionately versus the tube length, so that a wide adjustment range is already possible with relatively short tubes.
As paste-like liquids, silicones or silicone mixtures have until now proved to be especially suitable whose consistence can be adapted depending on the operating conditions. Due to the diversity of such substances, just about all conceivable conditions can be covered. Moreover, the composition of a silicone mixture will also provide a viscosity adjustment, so that additional adjustment possibilities for the discharge period will result.
In an advantageous further development of the invention, the downstream front end of the tube is connected to a collection vessel. The ejected substances are thus not released so that there will be no possible contaminations due to the paste-like liquid and its re-use will be possible. In any event, however, the paste-like liquid can be better subjected to a recycling process or a disposal if it is specifically collected and thus only slightly burdened with contaminations.
Other characteristics of the invention contribute to the sensor""s simple design and compact construction. Concerning the arrangement of working plunger and reservoir, it is proposed that the working plunger shortens the reservoir on the rear side in direction of the driving force and that the liquid is released on the front side. Thus, the arrangement of the outlet opening is largely independent of the sensor""s internal structure since the driving force applies from the opposite side, and the design in the area of the outlet opening remains unaffected thereby.
For its implementation, particularly two possibilities will result, i.e. one with bellows whose downstream rear end is displaced with its surfaces as parallel as possible to enable specific and complete ejection. Alternatively, the reservoir can also be designed as a cylinder, and the working plunger designed as a cooperating piston which presses the liquid out.
Two preferred embodiments are proposed for a spatial arrangement of power transmitter, reservoir and chamber. One is to forwardly arrange the reservoir which is open in direction of the driving force, and to arrange the power transmitter behind it. As a rule, there will be sufficient space, in this case, next to the power transmitter to provide the chamber there. However, a coaxial arrangement of power transmitter, reservoir and chamber is especially preferred in which the power transmitter moves in axial direction and is formed as a spring surrounding the chamber on the outside. For power transmission, the brake plunger can be advantageously connected to the power transmitter, indirectly via the working plunger, for example, via a rod which penetrates the chamber in axial direction.
Another concept also prefers a coaxial arrangement of power transmitter, reservoir and chamber in which the driving force applies in axial direction. However, in this case, the reservoir is radially surrounded outside by the chamber and by the power transmitter arranged behind the chamber in direction of the driving force which enables direct power transmission from the power transmitter to the chamber without further auxiliary means. In contrast, power transmission to the reservoir is rendered more difficult. Yet, even this compact arrangement enables a simple structure of the sensor.
In an advantageous embodiment of the invention, the brake plunger displaces the chamber""s rear side in direction of the driving force so that paste-like liquid is pressed through the tube due to the volume reduction. Simultaneously, the displaced volume outside the chamber will be free and can be filled, for example, with the discharged paste-like liquid. Thus, the tube can advantageously be attached to the rear side of the chamber and the paste-like liquid can be expelled into the vacated volume. Since the brake plunger presses in direction of the driving force, no power transmission mechanism will be required which is susceptible to repairs.
Like the reservoir, the chamber can also be designed as bellows or in a piston cylinder arrangement. In the bellows design, the brake plunger moves the rear side in direction of the driving force. However, a piston cylinder arrangement is preferred since the spacexe2x80x94displaced by the plunger""s movement relative to the cylinderxe2x80x94can be used, if suitably designed, as a collecting vessel for the paste-like liquid. To achieve relative movement, either the cylinder can be fixed and the piston be moved over the brake plunger, or the piston is fixed and the cylinder is moved over the brake plunger. In the last case, if the power transmitter is arranged next to the chamber, the power transmission will be simplified sincexe2x80x94for forming the brake plungerxe2x80x94the connecting elements to the power transmitter need only be formed on the cylinder. The power transmitter can be formed especially as a spring.
The power transmitter is preferably designed such that the driving force is approximately constant over the entire movement of the working cylinder. Thus, without additional compensation mechanisms, a uniform discharge speed of the reservoir can be achieved.
According to the forms of embodiments so far described, an extension of the adjusted discharge period is not possible since the tube""s shortening will always result in a faster discharge. Thus, the invention providesxe2x80x94in one advantageous embodimentxe2x80x94to separably attach the tube to the chamber so that it can be replaced by a longer one. An already shortened tube can thus be replaced by a longer one; however, the exchange can also be for a tube whichxe2x80x94due, for example, to a different cross-section distributionxe2x80x94permits a different adjustment range for the discharge period.
Furthermore, a method for the manufacture of the sensor according to the invention is proposed with the sensor first being provided with a tube of maximum length so that all adjustment possibilities of the discharge period are open. Only subsequentlyxe2x80x94for example, at the customer""s on location or even by the customer himselfxe2x80x94there will be an adjustment to the desired discharge period by cutting off a downstream front piece of the tube. Thus, except for the easily performable step of shortening the tube, sensors can be produced by a uniform method, for different discharge periods. No further explanation will be necessary with regard to the fact that this will result in considerable economic benefits. The tube can be shortened either by the sales personnel or even by the customer himself.
Another process characteristic relates to sensors where the tube is detachably connected to the chamber. For an adjustment of the discharge period, it is suggested to remove the tube and replace it by another.